This invention relates to a new category of thermal engine in which an external source of thermal energy supplies the working medium for a thermal cycle. The thermal cycle can be an open cycle in which the medium is exhausted and discharged from the engine or a closed cycle. In general, the state-of-the-art of external combustion engines, including rotary engines, is characterized by an intermittent cyclic heat release by periodic combustion within high-pressure chambers. Combustion is generally either spark ignited in the case of gasoline engines, or auto ignited in the case of high-pressured diesel engines in which fuel is periodically injected into the combustion chambers. These engines, whether utilizing recipical pistons or rotary pistons have certain limitations in providing efficient combustion and low pollution emission. Because of the periodic nature of combustion there are severe pressure limitations on the structure of the engine, and low power density and low thermal efficiency that results from the inability to have full and complete combustion within the extremely brief combustion phase of the operating cycle. Furthermore, fuel quality must be closely controlled to insure consistent operation. The use of high octane and cetane fuels to inhibit premature detonation and control the burning process in modern engines contributes to the release of exotic pollution emissions.
In addition, internal combustion engines that are of a gas turbine design are efficiently operable only within a narrow range of rotations and loads. Inefficiently high fuel consumptions must be maintained under partial load conditions to prevent a reduction in temperature and driving pressure with a resulting reduction in the level of rotation. This results in a drop of the pressure ratio and effects a substantial loss in efficiency. Furthermore, the very structure of a gas turbine engine is complex and expensive to fabricate, utilizing exotic materials and assemblies. This limits the use of such engines primarily to aircraft.
A primary object of this invention is to devise a engine that can utilize a relatively steady state, external thermal source to continuously generate a high-pressure, high-temperature motive gas to drive an engine and produce mechanical power for use in transportation or electrical energy production. Such an external heat engine can thereby utilize a variety of different sources of heat and grades of fuel to directly produce the motive gases. By the use of suitable heat exchange devices a variety of sources can heat a select motive gas to the temperatures and pressures necessary to endlessly supply the engine with its driving medium.